Spatio-temporal gradients in food supply help explain the short-term colonisation dynamics of the critically endangered central rock-rat (Zyzomys pedunculatus)

Currently, the impact of introduced predators on small mammal population decline is a focal research direction in the Australian desert literature. In all likelihood though, single-factor explanation of population dynamics is inadequate, leaving gaps in our knowledge of the multitude of potential influences on small mammal abundance and occupancy patterns in time and space. Here, we investigated floristic gradients across four potential refuge sites of the central rock-rat, Zyzomys pedunculatus, a granivore rodent (50-120 g) that is endemic to central Australia and is categorised as critically endangered. The study took place in Tjoritja/West MacDonnell National Park in the MacDonnell Ranges bioregion. Floristic sampling was allocated across the four sites, the locations of which were predetermined by an established monitoring and management programme for the central rock-rat. Our aim was to examine the relationship between environmental gradients and floristic composition across the four sites, and thereby test the extent to which the patterns of food type and food availability can inform central rock-rat spatio-temporal dynamics. We found high site-scale floristic patterning that related foremost to elevation and then to antecedent rainfall and time-since-fire and fire-severity effects. To interpret these results, we applied the principles of refuge theory and we described a gradient from core refuge habitat to intermittent and then marginal habitat within the current central rock-rat stronghold area. Overall, our results implied a strong floristic basis to central rock-rat site occurrence, and they thus compel us to take explicit account of spatial (elevation) and temporal (rainfall-productivity and fire-disturbance) influences on the food axis of potential refuge sites of this critically endangered species.